Method of pickling metallic strip



March 9, 1943.

R. A. DIMON METHOD OF PIGKLI-NG METALLIC STRIPv Filed April 28, 1939 Patented Mar. 9, 1943 -Richard A. Dimon, Pittsburgh, Pa., assigner to Carnegie-Illinois Steel Corporation, a corporation of New Jersey application April 28,1939, serial No. 270,703 1 claim. (ci. zot-145) y The present invention relates to a continuous method for the preparation of the surface of metallic strip.

In the coating of metallic surfaces, especially lin the electroplating thereof, it is well recognized that the properties of the resulting coating, in particular its adherence to the base metal, are greatly inuenced by the conditioning treat.- ments given the metallic surface prior to the coating operation. In the case of certain electrodeposited metallic coatings, for example tin, it is known that the base metal must be microroughened to a definite degree if a tightly adherent tin coating is to be obtained. In the past such roughening of the surface has been generally -obtained by pickling the metallic material in an acid solution, sufcient time being allowed for the acid not only to remove any oxide present but to actually chemically attack (etch) the surface to the desired degree. The time required in such a pickling step is of the order of a minute or two. In the plating of sheets or irregular shaped objects which operations are themselves slow, such a length of pickling time has not been objectionable. However, in lthe continuous plating of metallic strip, it has proved a serious handicap since the economic operation of the latter process requires the utilization of high processing speeds.

It is apparent that the necessary pickling time could be obtained in a high speed continuous strip plating operation by increasing the size of the acid solution container.

size, however, not only adds to the cost of the equipment but requires considerable floor space which is itself valuable,` and may not always be available.

While the use of an anodic pickling step would satisfy the time and space requirementsl of a high speed continuous strip operation, it has been experienced that such a step requires an excessive amount of control to avoid overpickling or' the surface of the strip. Said overpickling results in a coated product having poor appearance.

The danger of overpickling is especially prevalent in a process which slows down the strip to join incoming and outgoing ends.

Under the present method, the aforementioned disadvantages are overcome.

An object of the present invention resides in providing an initial concentrated electrochemical pickling action at the surface of the continuous- 1y moving metallic stripand immediately thereafter continuing the pickling while in the same pickling solution but in a purely' chemical manner.

Other objects and advantages will become apparent as the description proceeds and reference Such increase in is had to the accompanying drawing, in which:

'Ihe ilgure is a sectional elevation of the present invention.

The single gure of the drawing is a diagrammatic showing of a pickling tank and the manner in which the present invention is practiced therewith.

' In the drawing, the metallic strip S is continuously fed over a conductor roll 3 into the pickling tank 2. Immediately at its point .of entry into the pickling tank, the metallic strip is passed between two cathodcs t which are connected to the negative side of a generator 5. The conductor roll 3 over' which theincoming continuous metallic strip passes is connected'to the positive side of the generator so as to establish the metallic strip as the anode, whereby as it passes between the cathodes 4 positioned at the entrance end of the pickling tank 2, the strip is imme- 4 diately subjectedto a violent electrochemical pickling action. This initial violent pickling of the metallic .strip produces an active surface thereon which expedites the straight chemical action of the pickling' solution on said surface during its passage through the remaining portion of the pickling bath.

'I'he strip S, comprising base metal for tin plate or the like, is moved in a substantially vertical loop having ythe horizontal extent thereof, as by reason of the sinker roll shown in the drawing, relatively smaller or less than the vertical extent of said loop, whereby the pickling process may be effected within a minimum space in the direction of travel of the strip.

As a .result of the initial vigorous electropickling action,' underpickling, as would `result were the material subjected to straight chemical action for the same time and in equipment of the same size, is avoided. Sufficient anodic pickling is thus given the strip so as to permit the chemical Vaction of the acid in the succeeding portions of the tank to rapidly progress, whereby the high degree of control necessary to avoid overpickling as would be the case'with anodic pickling alone, is eliminated.

The pickling bath may comprise a five per cent sulphuric acid solution maintained substantially at room temperature, the electrochemical step being carried out at a current density of amperes per square foot. Heating of the lpickling solution which in the past has been generat the same time, provides for the timev factorl which is important in the high speed continuous treatment of metallic strip being f ed into and out of the pickling bath.

While I have shown and described a speciilc embodiment of the present invention, it will be seen that I do not Wish to be limited exactly thereto, since various modications may be made without departing from the scope of the invention, as dened by the following claim.

I claim:

The method of continuously pickling base metal strip for tin plate and the like, which includes moving the said stripin a substantially vertical loop through an effective pickling solution, said loop being characterized by having the horizontal extent thereof relatively smaller than its vertical extent, imparting to the strip a violent anodic pickling action atthe immediate point of its entry into the said pickling solution, continuing the violent anodic pickling action for only a portion of the length of downward vertical travel of the strip through the pickling solution, and discontinuing the violent anodic pickling action at a substantial distance from the end of the length of downward travel of the strip, the remainder of the length of travel o the strip being conducted through the pickling solution while subjected to a pickling action which is`entirely chemical, the said anodic and chemical pickling comprising the only pickling 20 to which the strip is subjected in said solution.

RICHARD A. DIMON. 

